Over-the-top (OTT) services involve services that ride on top of an existing network service provided by a network operator, where the OTT services don't require any business or technology affiliations with the network operator. For example, televisions (TVs), Digital Video Disk (DVD) players and video game consoles are being built with wireless connectivity such that they can “piggyback” on an existing wireless network and pull content from the Internet. OTT services are likely to have a significant role in the proliferation of Internet television and Internet-connected TVs. OTT services may include audio, video, data, voice and other services.
The Internet Protocol (IP) multimedia subsystem (IMS), defined by the 3rd Generation Partnership Project (3GPP), is an architectural framework for implementing IP-based telephony and multimedia services. IMS defines a set of specifications that enables the convergence of voice, video, data and mobile technology over an all IP-based network infrastructure. In particular, the IMS fills the gap between the two most successful communication paradigms—cellular and Internet technology, by providing Internet services everywhere using cellular technology in a more efficient way. Session Initiation Protocol (SIP) is the main protocol for the IMS. SIP is an application layer control (signaling) protocol for creating, modifying and terminating sessions with one or more participants.